This invention relates to marine bottom supported structures for offshore work operations in cold waters and more particularly to ice islands which are grounded on a marine bottom for use as work platforms in relatively shallow waters and to the method of constructing the same.
With the increasing search for petroleum and gas deposits, considerable interest has been focused on exploration and production efforts in the arctic and antarctic regions of the world. In these areas, deposits of petroleum and gas are often found offshore in shallow waters that are ice-covered through a good portion of the year. Conventional floating platforms are not well suited for operations in these waters.
Various types of bottom-secured platforms have been suggested for use in such ice covered water, including reenforced pile-mounted raised platforms and artificial islands constructed from bottom dredgings. These structures have been successful and have demonstrated the ability to survive the summer ice breakup such as occurs in waters off the Alaskan coast. Such devices, however, are expensive to construct and do not lend themselves to use for temporary work such as exploratory drilling.
Ideally, ice itself will serve as a material for the construction of artificial islands in cold regions, especially during the winter months of the arctic and antarctic year which may extend as long as 9 or 10 months. It is known that grounded ice islands may be constructed by depositing water over existing ice to thicken it until the mass of the thickened area is such that its draft is greater than the water depth and at least a portion of the thickened area is grounded on the marine bottom. Two such devices and the method for constructing them are described in U.S. Pat. Nos. 3,750,412 (Fitch, et al.) and 3,863,456 (Durning).
Ice islands appear to be feasible for use as work platforms from which to conduct operations such as temporary exploratory drilling and, under the proper circumstances even year-round drilling. Ice islands which have been proposed to date are deficient, however, in that they do not provide for the containment of formation fluids, such as crude petroleum, in the event of accidental escape from the formation during a drilling operation. Conventional ice islands are not adapted to cope with shifting ice and the stresses imposed on the island as a result thereof even though it is understood that ice shift may occur even during the winter months.
The present invention contemplates an ice island and the method for its construction which is designed to overcome the foregoing deficiencies.